Composition for preventing creeping of a flux for soldering

ABSTRACT

The present invention relates to a composition for preventing creeping of a flux for soldering, which is free from a problem from the viewpoint of the global environment or working environment. The present invention provides a composition for preventing creeping of a flux for soldering, consisting of a composition comprising a polymer containing polymer units of an unsaturated ester containing a polyfluoroalkyl group, a fluorine-type surfactant and an aqueous medium. Further, the present invention provides a method for soldering by means of the composition. Furthermore, the present invention provides an electronic part or printed board soldered by the method. Still further, the present invention provides an electric appliance employing such an electronic part or printed board.

TECHNICAL FIELD

The present invention relates to a composition to be used for pretreatment for soldering an electronic part having electric contact points or a printed board having electric contact points, which prevents creeping of a flux for soldering. Further, the present invention relates to a method for soldering by means of such a composition, an electronic part or printed board obtained by such a method, and further an electric appliance.

BACKGROUND ART

When various parts are to be soldered to a printed board, or IC is to be soldered to an IC socket, it is common to preliminarily treat the printed board with a flux in order to improve the adhesion of the solder. Usually, a flux contains an acidic component and thus is corrosive. Accordingly, it is necessary to prevent adhesion or penetration of a flux at an electric contact portion of an electronic part such as a connector, a switch, a volume or a pre-set resistor or at a portion where no soldering is required in a printed board. Especially in a case of an electronic part, soldering is frequently carried out at a through-hole portion. A phenomenon such that a flux creeps such a through-hole portion by e.g. a capillary phenomenon and penetrates or deposits at an unnecessary portion of the electronic part, is called “creeping of a flux”, and it is necessary to prevent such a phenomenon.

For the purpose of preventing penetration or deposition of the flux, an agent for preventing creeping of a flux is used. As agents for preventing creeping of a flux for soldering, the following examples are known.

(1) A composition containing a compound having a polyfluoroalkyl group or a polymer thereof, as an essential component (JP-A-60-49859). Such a composition contains, as a solvent, a hydrocarbon type solvent such as heptane, an ester type solvent such as ethyl acetate, a chlorofluorocarbon (CFC) such as 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), or a perfluorocarbon (PFC) having a boiling point of from 60 to 120° C., or a fluorine-containing aromatic hydrocarbon type solvent such as 1,3-bis(trifluoromethyl)benzene.

(2) A composition having a low molecular compound containing polyfluoroalkyl groups or a polymer containing polyfluoroalkyl groups, dissolved in an alcohol solvent such as ethanol.

(3) A composition having a fluorine polymer obtained by polymerizing tetrafluoroethylene, a perfluoro (alkylvinyl ether) or vinylidene fluoride, a surfactant and an extender, dispersed in water (JP-A-5-175642.

(4) An aqueous dispersion comprising a copolymer of C₈F₁₇SO₂N(CH₂CH₂)CH₂CH₂OCOCH═CH₂ with dodecyl methacrylate, and an emulsifier containing no fluorine (JP-A-62-149784).

However, conventional agents for preventing creeping of a flux for soldering, have the following problems.

The composition (1) requires a due care, since the organic solvent is inflammable, and further, it has a problem from the viewpoint of the working environment, since it contains a volatile solvent. Further, when the solvent is a hydrocarbon type solvent, there will be problem that the solubility of the fluorine-containing component in the composition is poor. Further, with respect to CFC among the solvents, its influence over the ozone layer is feared, and its use is restricted by regulations relating to fluorocarbons. HCFC-225 or HCFC-141b, as a substitute for CFC, has similar problems. Further, PFC has a high coefficient for warming up the earth, and its influence over the environment is feared. The fluorine-containing aromatic hydrocarbon type solvent is inflammable and has a problem of odor.

The composition (2) is required to have the fluorine content of the low molecular weight compound or the polymer lowered in order to increase the solubility of such a compound or a polymer in the alcohol solvent. Further, the effect for preventing creeping of a flux is inadequate.

The fluorine polymer in the composition (3) is non-adhesive and poor in wettability and adhesion to the surface of an electronic part as a substrate. Accordingly, it is practically required to add a spreader. Further, this fluorine polymer has a softening point higher than 150° C., and heat treatment at a high temperature is required in order to form a film by drying the fluorine polymer particles deposited on a substrate by means of a spreader. The temperature for this heat treatment will be higher than the heat resistant temperatures of most of parts having plastic portions, and practically, there is a problem that such heat treatment can not be done. On the other hand, if no heat treatment is applied, white solid fluorine polymer particles are likely to deposit as white solid on electronic parts, and there will be a drawback that the gloss of the treated surface is impaired.

The composition (4) has a problem that the surface tension is high and its wettability to the surface of electronic parts as substrates, is poor, and when it is practically coated on an electronic part, coating irregularities are likely to result. Further, when such a composition is deposited on an electric contact portion, there is a problem that electric conduction tends to be poor.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above problems and provides a composition for preventing creeping of a flux for soldering, which comprises a polymer (A) containing the following polymer units (a¹), a fluorine-type surfactant (B¹) and an aqueous medium (C), a method for soldering by means of the composition, an electronic part or printed board obtained by the method, and an electric appliance.

(a¹): Polymer units of an unsaturated ester containing a polyfluoroalkyl group, or polymer units of an unsaturated ester containing a polyfluoroalkyl group having an etheric oxygen atom inserted in the carbon-carbon bond.

BEST MODE FOR CARRYING OUT THE INVENTION

The polymer (A) in the present invention is a polymer containing specific constituting units i.e. polymer units (a¹).

In the following, a polyfluoroalkyl group and a polyfluoroalkyl group having an etheric oxygen atom inserted in the carbon-carbon bond, will be generally referred to as a “R^(f) group”. An alkyl group and an alkyl group having an etheric oxygen atom inserted in the carbon-carbon bond, will be generally referred to as an “alkyl group which may contain an etheric oxygen atom”. An acrylate and a methacrylate will be generally referred to as a (meth)acrylate, and the same applies to other (meth)acrylic acid, etc.

The polymer units (a¹) are polymer units of an unsaturated ester containing a R^(f) group.

The R^(f) group is meant for a group having at least two hydrogen atoms of an alkyl group which may contain an etheric oxygen atom, substituted by fluorine atoms. The number of fluorine atoms in the R^(f) group is preferably at least 60%, particularly preferably at least 80%, when it is represented by [(the number of fluorine atoms in the R^(f) group)/(the number of hydrogen atoms contained in the alkyl group which may contain an etheric oxygen atom, having a structure corresponding to the R^(f) group)]×100%.

Further, as the R^(f) group having an etheric oxygen atom, a R^(f) group containing an oxypolyfluoroalkylene moiety of e.g. oxypolyfluoroethylene or oxypolyfluoropropylene, may be mentioned.

The carbon number of the R^(f) group is preferably from 4 to 14, particularly preferably from 6 to 12. The R^(f) group may be of a straight chain structure or a branched structure, preferably of a straight chain structure. When it is of a branched structure, it is preferred that the branched moiety is present at a terminal portion of the R^(f) group and is a short chain with from 1 to 3 carbon atoms. Further, the R^(f) group may have a chlorine atom at the terminal portion. As the structure of the terminal portion of the R^(f) group, a structure such as CF₃CF₂—, CF₂H—, CF₂Cl— or (CF₃)₂CF— may be mentioned.

The R^(f) group in the present invention is preferably a perfluoroalkyl group (hereinafter referred to as a R^(F) group) which may contain an etheric oxygen atom, having substantially all hydrogen atoms of an alkyl group which may contain an etheric oxygen atom, substituted by fluorine atoms. The carbon number of the R^(F) group is preferably from 4 to 14, particularly preferably from 6 to 12. Further, the R^(F) group may be of a straight chain structure or a branched structure, preferably a group of a straight chain structure.

The R^(F) group is preferably a group having substantially all hydrogen atoms of an alkyl group substituted by fluorine atoms (i.e. a group containing no etheric oxygen atom), particularly preferably a straight chain group represented by F(CF₂)_(n)−[wherein n is an integer of from 6 to 12].

Specific examples of the R^(f) group include the following structures, but are not limited thereto. Further, in the following specific examples, groups corresponding to structurally isomeric groups, are included.

Examples of the R^(f) group containing no etheric oxygen atom.

C₂F₅—, C₃F₇— [including both F(CF₂)₃— and (CF₃)₂CF—], C₄F₉— [including F(CF₂)₄—, (CF₃)₂CFCF₂—, (CF₃)₃C— and F(CF₂)₂CF(CF₃)—], C₅F₁₁— [including structurally isomeric groups such as F(CF₂)₅—, (CF₃)₂CF(CF₂)₂—, (CF₃)₃CCF₂—, and F(CF₂)₂CF(CF₃)CF₂—], C₆F₁₃— [including structurally isomeric groups such as F(CF₂)₃C(CF₃)₂—], C₈F₁₇—, C₁₀F₂₁—, C₁₂F₂₅—, C₁₅F₃₁—, HC_(t)F_(2t)— (wherein t is an integer of from 1 to 18), (CF₃)₂CFC_(s)F_(2s)— (wherein s is an integer of from 1 to 15), etc.

Examples of the R^(f) group containing an etheric oxygen atom.

F(CF₂)₅OCF(CF₃)—, F[CF(CF₃) CF₂O]_(s)CF(CF₃) CF₂CF₂—, F[CF(CF₃)CF₂O]_(t)CF(CF₃)—, F[CF(CF₃)CF₂O]_(u)CF₂CF₂—, F(CF₂CF₂CF₂O)_(v)CF₂CF₂—, F(CF₂CF₂O)_(w)CF₂CF₂— (wherein s and t are independently an integer of from 1 to 10, preferably an integer of from 1 to 3, u is an integer of from 2 to 6, v is an integer of from 1 to 11, preferably an integer of from 1 to 4, and w is an integer of from 1 to 11, preferably an integer of from 1 to 6), etc.

The polymer units (a¹) in the present invention are preferably polymer units of a R^(f) group-containing (meth)acrylate represented by the following formula (1):

CH₂═CR¹COO—Q¹—R^(f)  (1)

provided that the symbols in the formula (1), have the following meanings.

Q¹: A single bond or a bivalent connecting group.

R¹: A hydrogen atom or a methyl group.

R^(f): R^(f) group.

Q¹ in the group is preferably a bivalent organic connecting group, particularly preferably those mentioned in the following specific examples. R^(f) in the formula is preferably a polyfluoroalkyl group containing no etheric oxygen atom, particularly preferably a perfluoroalkyl group containing no etheric oxygen atom. The following compounds may be mentioned as specific examples of the R^(f) group-containing (meth)acrylate represented by the formula (1).

F(CF₂)₈(CH₂)₂OCOCH═CH₂,

F(CF₂)₈(CH₂)₂OCOC (CH₃)═CH₂,

F(CF₂)₈(CH₂)₃OCOCH═CH₂,

F(CF₂)₇CH₂OCOCH═CH₂,

F(CF₂)₁₀(CH₂)₂OCOC(CH₃)═CH₂,

H(CF₂)₈(CH₂)₂OCOC(CH₃)═CH₂,

(CF₃)₂CF(CF₂)₆(CH₂)₂OCOC(CH₃)═CH₂,

F(CF₂)₈SO₂N(CH₂CH₂CH₃)—

—(CH₂)₂OCOCH═CH₂.

Polymer units (a¹) in the polymer (A) may be of one type only, or of two or more types. In the case of two or more types, they are preferably polymer units of two or more monomers having different carbon numbers in the R^(f) group portions.

The polymer (A) may contain polymer units other than the polymer units (a¹). The polymer units other than the polymer units (a¹) are not particularly limited, so long as they are polymer units of a monomer (hereinafter referred to as other monomer) having a polymerizable unsaturated group and no R^(f) group. Such other monomer may be employed from known or well known compounds, and one or more of them may be used. It is preferred to employ a polymer (A) containing polymer units of other monomer, since the leveling property will be improved, and the uniformity of the coating film will also be improved.

Such other monomer is preferably selected from polyolefin type unsaturated esters such as acrylic acid esters, unsaturated esters having epoxy groups, compounds having vinyl groups, compounds having amino groups and polymerizable unsaturated groups, and compounds having substituted amino groups and polymerizable unsaturated groups.

Further, the polymer (A) is preferably a polymer containing the following polymer units (a²) and/or the following polymer units (a³), together with the polymer units (a¹).

Polymer units (a²): Polymer units of at least one unsaturated compound selected from ethylene, vinyl chloride, styrene, (meth)acrylic acid, cyclohexyl (meth)acrylate, an alkyl (meth)acrylate, a mono(meth)acrylate of a polyoxyalkylene diol, and glycidyl (meth)acrylate.

Polymer units (a³): Polymer units of a compound having an amino group and a polymerizable unsaturated group, or polymer units of a compound having a substituted amino group and a polymerizable unsaturated group.

The polymer units (a²) have an effect of lowering the softening point of the polymer (A) to a proper temperature. Further, the polymer units (a³) have a nature of improving the spreadability of the polymer (A) or the leveling property of the coating film. When the polymer (A) contains no polymer units of other monomer, it is likely that no satisfactory leveling can be obtained, and the coating film may not be uniform. The substituted amino group in the polymer units (a³) is a group having one or two hydrogen atoms of an amino group substituted by a monovalent substituent. Such a monovalent substituent is preferably an aliphatic hydrocarbon group, particularly an alkyl group, most preferably a C₁₋₆ alkyl group. In the following, an amino group and a substituted amino group will generally be referred to as an “amino group which may be substituted”. As the amino group which may be substituted, a dimethylamino group, a monomethylamino group, a monoethylamino group or a diethylamino group, may, for example, be preferred.

Polymer units (a³) are preferably polymer units of a compound having an amino group which may be substituted and a (meth)acryloyl group, particularly preferably, polymer units of a compound represented by the following formula (2).

CH₂═CR²CO—Q²—NR¹⁰R¹¹  (2)

provided that the symbols in the formula have the following meanings.

R²: A hydrogen atom or a methyl group.

R¹⁰, R¹¹: Independently, a hydrogen atom or a C₁₋₆ alkyl group.

Q²: A single bond or a bivalent connecting group.

When each of R¹⁰ and R¹¹ in the formula (2) is a C₁₋₆ alkyl group, a methyl group, an ethyl group or an isopropyl group is preferred. Each of R¹⁰ and R¹¹ which are independent of each other, is preferably a hydrogen atom, a methyl group or an ethyl group, and it is particularly preferred that one of R¹⁰ and R¹¹ is a methyl group or an ethyl group. As specific examples of Q², those in the following compounds may be mentioned, and a single bond or an oxyethylene group is preferred. Specific examples of the formula (2) will be given below.

CH₂═CHCOO(CH₂)₂N(CH₃)₂,

CH₂═CHCOO(CH₂)₂N(CH₂CH₃)₂,

CH₂═CHCON(CH₃)₂,

CH₂═C(CH₃)CON(CH₂CH₃)₂,

CH₂═CHCONH(CH₂)₃N(CH₃)₂,

CH₂═CHCONHCH(CH₃)₂,

When the polymer (A) is a copolymer containing polymer units (a²), the proportion of the polymer units (a¹) in the polymer (A) is preferably from 60 to 99 wt %, particularly preferably from 70 to 95 wt %. When the polymer (A) is a copolymer containing polymer units (a³), the proportion of the polymer units (a¹) in the polymer (A) is preferably from 55 to 99 wt %, particularly preferably from 70 to 90 wt %. If the proportion of the polymer units (a¹) is low, the surface tension of the coating film surface will not decrease, and the performance for preventing creeping of a flux is likely to be inadequate.

The proportion of the polymer units (a²) in the polymer (A) is preferably from 1 to 40 wt %, particularly preferably from 10 to 30 wt %. The proportion of the polymer units (a³) in the polymer (A) is preferably from 1 to 50 wt %, particularly preferably from 10 to 30 wt %.

As the polymer units (a²), preferred are polymer units of (meth)acrylic acid, cyclohexyl (meth)acrylate, an alkyl (meth)acrylate, a mono(meth)acrylate of a polyoxyalkylene diol, or glycidyl (meth)acrylate, and particularly preferred are polymer units of an alkyl (meth)acrylate As the alkyl (meth)acrylate, preferred is an alkyl (meth)acrylate wherein the carbon number of the alkyl group portion is at least 6, and particularly preferred is 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate or behenyl (meth)acrylate.

The polymer (A) of the present invention is preferably a polymer containing the polymer units (a²) and the polymer units (a³) together with the polymer units (a¹). The polymer (A) may contain polymer units other than the polymer units (a¹), (a²) and (a³), but in the present invention, preferably contains no such other polymer units.

The fluorine content in the polymer (A) is preferably at least 30 wt %, particularly preferably at least 45 wt %, most preferably from 45 to 80 wt %. If the fluorine content is less than 30 wt %, the critical surface tension of the surface of the coating film formed after the treatment tends to be high, whereby no adequate performance for preventing creeping of a flux, tends to be obtained.

The average molecular weight of the polymer (A) is preferably from 1×10³ to 1×10⁷, particularly preferably from 1×10⁴ to 1×10⁵, most preferably from 2×10⁴ to 5×10⁴. Further, when the polymer (A) is a polymer containing at least two types of polymerizable units, the arrangement of the respective polymer units may be block or random, particularly preferably random.

The composition of the present invention contains a fluorine type surfactant (B¹) and an aqueous medium (C) together with the polymer (A). The polymer (A) in the composition is preferably dispersed in the form of particles in the after-described aqueous medium. The particle size of particles dispersed in the composition is preferably from 0.01 to 1 μm. The concentration of the polymer (A) in the composition of the present invention is preferably from 0.01 to 3 wt %, particularly preferably from 0.03 to 1 wt %. If the concentration of the polymer (A) is less than 0.01 wt %, no adequate effect for preventing creeping of a flux tends to be obtained, and if the concentration is higher than 3 wt %, the coating film of the polymer (A) to be formed at the time of treatment, tends to be so thick that the solder is likely to be hardly attached.

The composition of the present invention contains the above polymer (A) as an essential component. When the composition is to be treated by a usual treating method, the composition is applied to the surface of an electronic part and then dried to soften the polymer (A) to form a uniform coating film.

For the composition of the present invention to be widely used, the softening point of the polymer (A) is preferably low. The heat resistant temperatures of plastics to be used for electronic parts, are about 150° C. in most cases, and the softening point of the polymer (A) is accordingly preferably lower than 150° C. Further, taking also the drying efficiency into consideration, the softening point of the polymer (A) is preferably at least 40° C. and less than 150° C., particularly preferably from 80 to 120° C.

In the present invention, the surface tension of the composition can be adjusted to from 10 to 25 dyn/cm (20 to 30° C.) by incorporating the above polymer (A) and the fluorine type surfactant (B¹) in combination to the composition. Usual surface tension of an aqueous dispersion of the polymer (A) containing no fluorine type surfactant (B¹), is at a level of from 40 to 70 dyn/cm (20 to 30° C.). On the other hand, the critical surface tension of a substrate to which the composition of the present invention can be applied, usually becomes at a level of from 25 to 40 dyn/cm. Accordingly, the surface tension of the composition of the present invention containing the fluorine type surfactant (B¹) becomes lower than the surface tension of the substrate, and thus, it is excellent in wettability or adhesion to the substrate and exhibits a performance for preventing creeping of a flux.

The aqueous dispersion of the polymer (A) containing the polymer units (a³) may have a low surface tension even without containing the fluorine type surfactant (B¹). However, by an addition of the fluorine type surfactant (B¹), the surface tension can further be decreased.

As the fluorine type surfactant (B¹), an ionic surfactant having fluorine atoms, or a nonionic surfactant having fluorine atoms, may be mentioned.

Further, the fluorine type surfactant (B¹) may be any one of an anionic fluorine type surfactant having R^(f) groups and anionic groups in combination, a cationic fluorine type surfactant having R^(f) groups and cationic groups in combination, an amphoteric surfactant having R^(f) groups and cationic and anionic groups in combination, and a nonionic surfactant having R^(f) groups and hydrophilic groups in combination.

As tradenames of fluorine type cationic surfactants, “Surflon S-121”, manufactured by Asahi Glass Company Ltd., “Fluorade FC-134”, manufactured by 3M Co. and “Megafac F-150”, manufactured by Dainippon Ink & Chemicals Inc., may be mentioned.

As tradenames of fluorine type anionic surfactants, “Surflon S-111”, manufactured by Asahi Glass Company Ltd., “Fluorade FC-143”, manufactured by 3M Co. and “Megafac F-120”, manufactured by Dainippon Ink & Chemicals Inc., may be mentioned.

As tradenames of fluorine type amphoteric surfactants, “Surflon S-132”, manufactured by Asahi Glass Company Ltd., “Fluorade FX-172”, manufactured by 3M Co. and “Megafac F-120”, manufactured by Dainippon Ink & Chemicals Inc., may be mentioned.

As tradenames of fluorine type nonionic surfactants, “Surflon S-145”, manufactured by Asahi Glass Company Ltd., “Fluorade FC-170”, manufactured by 3M Co. and “Megafac F-141”, manufactured by Dainippon Ink & Chemicals Inc., may be mentioned.

The amount of the fluorine type surfactant (B¹) is preferably from 20 to 2,000 ppm, particularly preferably from 100 to 1,000 ppm, in the composition. If the amount of the fluorine type surfactant (B¹) is made at least 20 ppm, the wettability of the composition to a substrate and the performance for preventing creeping of a flux, can be improved. On the other hand, by adjusting it to at most 2,000 ppm, the critical surface tension of the formed coating film tends to be low, and an adequate performance for preventing creeping of a flux can be obtained. When the fluorine type surfactant (B¹) is used in a large amount, the fluorine type surfactant (B¹) tends to remain on the surface of the coating film, whereby the critical surface tension tends to be high, and the desired performance may not be obtained. In such a case, the treated substrate may be rinsed with water to remove the surfactant on the coating film surface. However, two additional steps of rinsing and redrying will then be required, such being undesirable.

Further, the composition of the present invention contains an aqueous medium (C). As the aqueous medium (C), water, or one having a water-soluble organic solvent incorporated to water, may be mentioned. As the water-soluble organic solvent, a ketone, an ester, a glycol, a glycol ether or an alcohol may, for example, be mentioned. When the aqueous medium (C) contains a water-soluble organic solvent, the proportion of water in the aqueous medium (C) is preferably from 50 to 95 wt %, while the proportion of the water-soluble organic solvent is preferably from 5 to 50 wt %.

Further, the water-soluble organic solvent is preferably one having a boiling point of from 40 to 200° C, from the viewpoint of drying efficiency. Further, the aqueous medium (C) is preferably an organic solvent which has a solubility in water at 20° C. of at least 1 wt %. Further, the amount of the aqueous medium (C) in the composition is preferably from 5 to 50 wt %, particularly preferably from 10 to 30 wt %.

The method for preparing the polymer (A) of the present invention is not particularly limited. When it is synthesized by an emulsion polymerization method, the composition of the present invention may directly be obtained, such being preferred. When the emulsion polymerization is carried out, it is preferably carried out by the following method 1 or 2.

Method 1: A method which comprises emulsifying a monomer in the presence of a medium and an emulsifier, followed by polymerization with stirring.

Method 2: A method which comprises emulsifying a monomer in the presence of a medium and an emulsifier by a homomixer or high pressure emulsifying apparatus, prior to addition of a polymerization initiator, and then reacting a polymerization initiating source for polymerization.

In either one of the above methods, when a monomer of gas state such as vinyl chloride is employed as the monomer, it may be continuously supplied under pressure by means of a pressure container. The polymerization initiating source is not particularly limited, and a usual polymerization initiator such as an organic peroxide, an azo compound or a persulfate, or ionizing radiation rays such as γ-rays, may, for example, be employed. As the medium, the same as the aqueous medium (C) may preferably be employed.

Namely, when the composition of the present invention is prepared by an emulsion polymerization method, it is preferred to employ a method wherein the compound represented by the formula (1) and other monomers, as the case requires, are emulsion-polymerized in the presence of an emulsifier in an aqueous medium (C).

Further, in all of the above-mentioned methods, the emulsifier may be the fluorine type surfactant (B¹) or the non-fluorine type surfactant (B²). It is preferred to employ the non-fluorine type surfactant (B²), since it is excellent in the emulsifying activity.

The composition of the present invention preferably contains the non-fluorine type surfactant (B²). Accordingly, it is preferred to prepare it by adding the fluorine type surfactant (B¹) without removing the non-fluorine type surfactant (B²) after the emulsion polymerization.

As the non-fluorine type surfactant (B²), a non-fluorine type non-ionic surfactant having a HLB value of at least 7, a non-fluorine type cationic surfactant having an alkyl group of at least 6 carbon atoms in its molecule, or a non-fluorine type anionic surfactant having an alkyl group having at least 6 carbon atoms in its molecule, is preferred.

As the non-fluorine type non-ionic surfactant having a HLB value of at least 7, a known nonionic surfactant having at least 5 oxyalkylene units in its molecule, is preferred. As the oxyalkylene units, oxyethylene or oxypropylene is preferred. Further, as the non-fluorine type cationic surfactant having an alkyl group of at least 6 carbon atoms in its molecule, an alkyl ammonium salt may, for example, be mentioned, and as the non-fluorine type anionic surfactant having an alkyl group of at least 6 carbon atoms in its molecule, an alkyl sulfate may, for example, be mentioned.

Now, specific examples of the non-fluorine type surfactant (B²) in the present invention will be given below.

Polyoxyethylene lauryl ether (HLB=14.5, oxyethylene addition mols=9), polyoxyethylene polyoxypropylene cetyl ether (HLB=9.5, oxyethylene addition mols=1, oxypropylene addition mols=8), polyoxyethyleneoctylphenyl ether (HLB=11.5, oxyethylene addition mols=10), polyoxyoxyethylenenonylphenyl ether (HLB=8.0, oxyethylene addition mols=5), stearyl trimethylammonium chloride, dioctyldimethylammonium chloride, lauryl ammonium sulfate, polyoxyethylenelauryl ether sodium sulfate, dimethyloctyldecylamine acetate.

Among these, preferred as the non-fluorine type surfactant (B²), is, for example, polyoxyethylenelauryl ether, polyoxyethyleneoctylphenyl ether, polyoxyethylenenonylphenyl ether, or dimethyloctyldecylamine acetate.

Further, when a surfactant is used during the emulsion polymerization, either the fluorine type surfactant (B¹) or the non-fluorine type surfactant (B²) may be used, or at least two surfactants having different ionic natures may be used in combination. However, when surfactants having different ionic natures, are used, it is preferred to combine cationic and non-cationic surfactants, anionic and nonanionic surfactants, or nonionic and amphoteric surfactants.

The composition of the present invention preferably contains the non-fluorine type surfactant (B²) together with the fluorine type surfactant (B¹), and the amount of the non-fluorine type surfactant (B²) is preferably from 50 to 80 wt %, based on the total amount of the fluorine-type surfactant (B¹) and the non-fluorine type surfactant (B²). The non-fluorine type surfactant (B²) may be the one used in the emulsion polymerization or may be added after the polymerization.

Further, the polymer (A) may be solution-polymerized by means of a fluorine-containing solvent. As the fluorine-containing solvent, HFC such as 1,3-bis(trifluoromethyl)benzene or 2,3-dihydrodecafluoro-(n-)pentane, or HCFC such as C₃HF₅Cl₂ (“AK-225”, tradename, manufactured by Asahi Glass Company Ltd.), may be mentioned. It is preferred that such a fluorine-containing solvent is removed after the polymerization, and the polymer (A) is dispersed in the aqueous medium (C) in the presence of the fluorine type surfactant (B¹) to obtain the composition of the present invention.

The composition of the present invention is diluted to an optional concentration depending upon the purpose and the application, and then applied to an article to be treated. As the treating method, a common method for coating may be employed. For example, a method such as dip coating, spray coating or coating by an aerosol can having the composition of the present invention packed therein, may be mentioned.

As the article to be treated, an electronic part having an electric contact, such as a connector, a switch, a volume or a pre-set resistor, or a printed board having an electric contact, may be mentioned. As the portion treated by the composition of the present invention, a portion may be mentioned where creeping of a flux is likely to take place during soldering of an electronic part such as a connector to a printed board. More specifically, a basal portion of an electronic part such as a connector, to be attached to a printed board, a board surface on the side of the printed board on which the electronic part is to be mounted, or a through-hole provided in a printed board to attach an electronic part, may, for example, be mentioned. By the treatment with the composition of the present invention, it is possible to prevent deposition of a flux for soldering at an unnecessary portion.

Further, the composition of the present invention provides a merit such that even when deposited at the contact portion, it does not impair the electric characteristics (such as electrical conductivity, etc.) or the outer appearance of the part. Accordingly, it may be applied over the entire surface of the electronic part or the printed board, and a treating method other than as described above, may be employed. For example, a treating method by total dipping or semi dipping with good treating efficiency, may be employed and preferred.

When the composition of the present invention is applied by total dipping, there is the optimum concentration of the polymer (A) for every type of the electronic part as the article to be treated. The optimum concentration range of the polymer (A) in the composition in the case of the total dipping treatment, may be shown in Table 1 for each type of the electronic part.

TABLE 1 Optimum concentration Type of the part range of polymer (A) Switch 0.03 to 0.3 wt% Volume 0.03 to 0.3 wt% Pre-set resistor 0.03 to 0.3 wt% Connector 0.05 to 1.0 wt% Printed board 0.20 to 1.0 wt%

Optimum concentration as shown in Table 1 is present for the following reason. Namely, when the composition is applied by total dipping, the composition will deposit not only at the desired portion (such as only the lead wire portion) but also at other portions, to form a coating film derived from the composition. On the other hand, with the electronic part to be an article to be treated, the contact load of the electric contact required for electrical conduction is different depending upon the type or the shape. Accordingly, by adjusting the concentration of the composition of the present invention, the film thickness can be adjusted so that the coating film may be removed by the load at the time of installing the electronic part.

Further, in the semi dipping method wherein only an electronic part which requires treatment, is dipped in the composition of the present invention, the optimum concentration range of the polymer (A) for the electronic part is preferably at most 3 wt % in the composition, particularly preferably from 0.01 to 0.3 wt %, with respect to any electronic part.

The composition of the present invention is applied to the surface of an electronic part or a printed board to be soldered, followed by drying to form a coating film on the surface. After the application, it is dried and preferably further subjected to curing. By the curing, it is possible to form a more uniform coating film on the surface of the treated article. The curing temperature is preferably a temperature exceeding the softening point of the polymer (A).

The composition of the present invention may contain other compounds within a range not to adversely affect the dispersion stability, the effect for preventing creeping of a flux, the insulating property for the outer appearance. As such other compounds, a pH controlling agent to prevent corrosion, a rust-preventing agent, a dye for controlling the concentration of the polymer in liquid, a stabilizer for the dye, a flame retardant, and an antistatic agent, may, for example, be mentioned.

The composition of the present invention serves to form a coating film on the surface of an electronic part or a printed board and to prevent creeping of a flux for soldering. And, an electronic part or a printed substrate, having corrosion by a flux prevented, will be presented.

The electronic part or the printed board, having a coating film formed on the surface by drying the composition of the present invention, will then be treated with a flux for soldering, followed by soldering, whereby a soldered electronic part or printed board will be presented. And, such an electronic part or printed board will be used for various electric appliances. Such electric appliances will be electric appliances with excellent quality, having a trouble to be caused by corrosion by a flux prevented. Specific examples of such electric appliances include equipments for computers, televisions, audio equipments (for equipments to be used for radio cassettes, compact discs, mini discs, etc.), portable telephones, etc.

The mechanism for the excellent performance of the composition of the present invention is not clearly understood, but is assumed to be as follows. Namely, by the interaction between the polymer (A) and the fluorine type surfactant (B¹) contained in the composition, the surface tension of the liquid lowers, whereby the wettability is improved, and a uniform coating film is formed by the composition. Further, the softening point of the polymer (A) is properly adjusted, whereby the quality of the coating film is improved. Further, during drying of the composition, the R^(f) groups in the polymer (A) will align regularly on the film surface to provide the performance efficiently.

EXAMPLES

Now, the present invention will be described in detail, but the present invention is not limited thereto.

Here, the molecular weight is a value measured by a gel permeation chromatography (GPC) and calculated as polystyrene. The softening point is a value measured by a Durrans mercury method.

Example 1

Preparation Example of Polymer A

Into a 1 liter autoclave made of glass, 167 g of F(CF₂)₈(CH₂)₂OCOCH═CH₂, 42 g of cyclohexyl methacrylate, 21 g of polyoxyethyleneoctylphenyl ether (oxyethylene addition mols=10, HLB=11.5), 1 g of dodecylmercaptan, 52 g of acetone and 365 g of deionized water, were added, and pre-emulsification was carried out at 50° C. for 1 hour. Then, 2 g of 2,2′-azobis(2-methylpropionamidine) hydrochloride was added, and the autoclave was flushed with nitrogen.

The temperature was raised to 60° C. with stirring, and polymerization was carried out for 15 hours. After cooling, the analysis was made by gas chromatography (GC), whereby the conversions of both F(CF₂)₈(CH₂)₂OCOCH═CH₂ and cyclohexyl methacrylate were at least 99%, and thus, the polymerization reaction was found to have proceeded satisfactorily. Then, filtration was carried out by means of a filter with a pore diameter of 6 μm to obtain a milky white emulsion. The solid content concentration of the emulsion was 30%, and the particle size of dispersed particles was 0.4 μm. Further, the average molecular weight of the copolymer was 3×10⁴, the softening point was 130° C., and the fluorine content was 49 wt %.

Example 2

Preparation Example of Polymer A

A polymerization reaction was carried out under the same conditions as in Example 1 except that cyclohexyl methacrylate was changed to behenyl methacrylate. After cooling, the analysis was carried out by GC whereby the conversions of both F(CF₂)₈(CH₂)₂OCOCH═CH₂ and behenyl methacrylate were at least 99%, and thus the polymerization reaction was found to have proceeded satisfactorily. Then, filtration was carried out by means of a filter with a pore diameter of 6 μm to obtain a milky white emulsion. The solid content concentration of the emulsion was 34%, and the particle size of the dispersed particles was 0.3 μm. Further, the average molecular weight of the copolymer was 2×10⁴, the softening point was 100° C., and the fluorine content was 47 wt %.

Example 3

Preparation Example of Polymer A

A polymerization reaction was carried out under the same conditions as in Example 1 except that cyclohexyl methacrylate was changed to CH₂═C(CH₃)COO(CH₂CH₂O)₄H, and polyoxyethyleneoctylphenyl ether was changed to dimethyloctadecylamine acetate. After cooling, the analysis was carried out by GC, whereby the conversions of both F(CF₂)₈ (CH₂)₂OCOCH═CH₂ and CH₂═C(CH₃)COO(CH₂CH₂O)₄H were at least 99%, and thus, the polymerization reaction was found to have proceeded satisfactorily. Then, filtration was carried out by means of a filter with a pore diameter of 6 μm to obtain a milky white emulsion. The solid content concentration of the emulsion was 32%, and the particle size of the dispersed particles was 0.2 μm. Further, the average molecular weight of the copolymer was 2×10⁴, the softening point was 110° C., and the fluorine content was 48 wt %.

Example 4

Preparation Example of Polymer A

Into a 1 liter autoclave made of glass, 167 g of CF₃(CF₂)₇(CH₂)₂OCOCH═CH₂, 42 g of N,N-dimethylaminoethyl methacrylate, 21 g of polyoxyethyleneoctylphenyl ether (oxyethylene addition mols=10, HLB=11.5), 1 g of dodecylmercaptan, 52 g of acetone, and 365 g of deionized water, were added, and pre-emulsification was carried out at 50° C. for 1 hour. Then, 2 g of azobis(methylpropionamidine) hydrochloride was added, and the autoclave was flushed with nitrogen. The temperature was raised to 60° C. with stirring, and polymerization was carried out for 15 hours. After cooling, the GC analysis was carried out, whereby the conversions of both CF₃(CF₂)₇(CH₂)₂OCOCH═CH₂ and N,N-dimethylaminoethyl methacrylate were at least 99%, and thus, the polymerization reaction was found to have proceeded satisfactorily. Then, filtration was carried out by means of a filter with a pore diameter of 6 μm to obtain a milky white emulsion. The solid content concentration of the emulsion was 34%, and the particle size of the dispersed particles was 0.1 μm. Further, the average molecular weight of the copolymer was 3×10⁴, and the softening point was 110° C.

Example 5

Preparation Example of a Comparative Polymer

Into a 1 liter beaker made of glass, 20 g of a ethylene tetrafluoride resin having an average molecular weight of 1×10⁴ and a softening point of at least 200° C., 10 g of casein calcium as an spreader, 3 g of polyoxyethyleneoctylphenyl ether (oxyethylene addition mols=10, HLB=11.5), and 80 g of deionized water, were added, and emulsification was carried out at 50° C. for 1 hour, to obtain a white emulsion having a solid content concentration of 33% and a particle size of 0.5 μm.

Preparation of Compositions 1 to 8

To the emulsions prepared in Examples 1 to 5, fluorine type surfactant compositions of the types and amounts (unit: wt %) as identified in Table 2, and deionized water were blended to obtain compositions 1 to 8 having a copolymer concentration of 1 wt %. Here, compositions 5 to 8 are comparative compositions. Here, Surflon S-145 is a composition comprising water and a fluorine type nonionic surfactant (30 wt %), and Surflon S-121 is a composition comprising water and a fluorine type cationic surfactant (30 wt %).

TABLE 2 Fluorine type surfactant Compo- Emulsion composition Deionized sition Type Amount Type Amount water 1 Example 1 3.3 S-145 3.3 93.4 2 Example 2 3.0 S-145 3.3 93.7 3 Example 3 3.0 S-121 3.3 93.7 4 Example 4 3.0 S-145 3.3 93.7 5 Example 1 3.3 Nil 0 96.7 6 Example 2 3.0 Nil 0 97.0 7 Example 3 3.0 Nil 0 97.0 8 Example 5 3.0 S-145 3.3 93.7

Method for Evaluating the Performance and Evaluation Results

(1) Wettability

To evaluate the wettabilities of compositions 1 to 8, the surface tensions at room temperature were measured by a Wilhelmy surface tension meter. The results (unit: dyn/cm) are shown in Table 3.

(2) Evaluation of film-forming property

Compositions 1 to 8 were coated on a non-soldered side of a printed substrate having 2,000 through-holes per sheet and then heat-treated at 120° C. for 5 minutes to remove water and to form coating films. The surface conditions of the coating films were visually inspected and evaluated under the following standards. The results are shown in Table 3.

A: Film with a uniform thickness and gloss on the surface.

B: Film with a non-uniform thickness without gloss on the surface.

C: Film whitened entirely.

(3) Evaluation of the performance for preventing creeping of a flux (first evaluation)

Into a container, a flux was put to a depth of about 2 mm, and five printed boards having coating films formed on their surfaces, prepared in (2), were placed thereon and left to stand for 1 minute. 1 Minute later, whether or not the flux creeped through the through-holes of the printed boards, was visually inspected, and the total number of holes where creeping was observed, was counted. The results are shown in Table 3.

(4) Evaluation of the deposition (contact angle) of a flux

Each of compositions 1 to 8 was diluted with a 10 wt % ethanol aqueous solution so that the copolymer concentration polymer concentration became 0.2 wt %. 20 Silver-plated phosphor bronze plates as usual materials for switches, were prepared, and they were dipped in the diluted compositions 1 to 8, respectively. Further, heat treatment was carried out at 120° C. for 5 minutes to form coating films on their surfaces.

5 Silver-plated phosphor bronze plates were selected, and the contact angles of the flux on their surfaces were measured by a droplet type projection contact angle meter manufactured by Kyowa Kaimen Kagaku K.K. The average value of the contact angles is shown in Table 4.

(5) Evaluation of contact resistance

15 Silver-plated phosphor bronze plates having coating films formed, as prepared in (4), were selected, and the contact resistance was measured by a three terminal method using a 1 mm semispherical measuring probe by a contact resistance meter manufactured by KS Buhin Kenkyusho. The measurement was carried out in a room wherein the temperature was controlled to be 23° C. by an air conditioner, and the contact load was 10 gf, and the number of measuring points was five points per sample (total of 75 points). A contact resistance of at most 100 mΩ was regarded as “satisfactory”, and the number of satisfactory measured points was obtained. The results are shown in Table 4.

(6) Evaluation of electrical conductivity

Diluted compositions 1 to 8 were coated by dipping in the same manner as in (4) except that 20 tact switches were used instead of the silver-plated phosphor bronze plates. They were soldered to a printed board, whereupon presence or absence of conduction failure was examined. The number of tact switches where conduction failure was observed, is shown in Table 4.

(7) Evaluation of the performance for preventing creeping of a flux (second evaluation)

The tact switch used for the evaluation in (6) was removed from the printed board and disassembled not to impair the surface condition of the lead-wire portion, whereupon presence or absence of creeping of the flux, was visually evaluated. The number of tact switches having lead wires where the creeping was observed, was counted. The results are shown in Table 4.

TABLE 3 Total number of holes Surface Film forming where creeping was Composition tension property observed 1 20 A 0 hole 2 21 A 0 hole 3 19 A 0 hole 4 20 A 0 hole 5 42 B 464 holes 6 43 B 535 holes 7 47 B 720 holes 8 45 C 884 holes

TABLE 4 Number of Number of tact tact switches Satisfactory switches where Contact points in having creeping Compo- angle of contact conduction was sition flux resistance failure observed 1 61 degree 75 points 0 0 2 61 degree 75 points 0 0 3 63 degree 75 points 0 0 4 62 degree 75 points 0 0 5 38 degree 56 points 2 2 6 33 degree 42 points 4 4 7 37 degree 62 points 3 3 8 28 degree 35 points 5 13 

INDUSTRIAL APPLICABILITY

The composition of the present invention is a non-flammable aqueous composition free from a trouble of destruction of the ozone layer or warming up the earth. With said composition, there is no substantial problem of odor, which is very advantageous from the viewpoint of working environment.

With said composition, even when applied by efficient dip coating, the coating film formed, is excellent in the outer appearance and also in the uniformity of the film thickness. Accordingly, simply by adjusting the concentration of the components of the composition, a coating film having a proper film thickness can be formed, and conduction failure can be prevented. Further, it is excellent also in the wettability of a flux, and a conventional treating method can be employed. Further, the composition of the present invention exhibits an excellent performance for preventing creeping of a flux. 

What is claimed is:
 1. A method for soldering an electronic part or printed board, comprising: forming a coating film by drying a composition on the surface of an electronic part or on the surface of a printed board, then treating the surface having the coating film thus formed, with a flux for soldering, and then carrying out soldering; wherein said composition comprises a polymer, a fluorine-containing surfactant and an aqueous medium; wherein said polymer contains a first polymer unit; wherein said first polymer unit is a polymer unit of an unsaturated ester containing a polyfluoralkyl group, or a polymer unit of an unsaturated ester containing a polyfluoroalkyl group having an etheric oxygen atom inserted in the carbon-carbon bond.
 2. A soldered electronic part or printed board, obtained by the method as defined in claim
 1. 3. An electric appliance employing the electronic part or printed board as defined in claim
 2. 4. The method according to claim 1, wherein said first polymer unit is represented by formula (1): CH₂═CR¹COO—Q¹—R^(f)  (1) wherein Q¹ is a single bond or a bivalent connecting group; R¹ is a hydrogen atom or a methyl group; and R^(f) is a polyfluoralkyl group, or a polyfluoroalkyl group having an etheric oxygen atom inserted in the carbon-carbon bond.
 5. The method according to claim 1, wherein said polymer further contains a second polymer unit and/or a third polymer unit; wherein said second polymer unit is a polymer unit of at least one unsaturated compound selected from the group consisting of ethylene, vinyl chloride, styrene, (meth)acrylic acid, cyclohexyl (meth)acrylate, an alkyl (meth)acrylate, a mono(meth)acrylate of a polyoxyalkylene diol and glydicyl (meth)acrylate; and wherein said third polymer unit is a polymer unit of a compound having an amino group and a polymerizable unsaturated group, or a polymer unit of a compound having a substituted amino group and a polymerizable unsaturated group.
 6. The method according to claim 1, wherein said composition further contains a non-fluorine-containing surfactant.
 7. The method according to claim 1, wherein a softening point of said polymer is at least 40° C. and less than 150° C.
 8. The method according to claim 1, wherein said aqueous medium contains a water-soluble organic solvent; and wherein a boiling point of the water-soluble organic solvent is from 40 to 200° C.
 9. The method according to claim 1, wherein a surface tension of the composition is from 10 to 25 dyn/cm. 